Against the background of increasingly interlinked production processes and their standardization in the industry, the problem that is nowadays the prime concern in the production of machine tools is that of also incorporating in this process the computer systems that are necessary for activating the machine tools. In this respect, one aim is to provide, to the extent technically possible, standardized machine control systems, offering the user greatest possible uniformity of the machine control parameters for the products from his range of workpieces—for instance when changing an actual machine type or else for improved data storage and archiving.
Such initiatives have already been pursued for some time for various types of machine tool, including for instance for bevel gear cutting machines, which are the focus of attention here.
For bevel gear cutting machines there are for instance solutions to this in which the relevant machine control parameters of an entire machine family are combined in a standardized data model with all the axes to be activated that come into consideration in the machine family, which then, in individual cases, is replicated on the respective machine actually concerned—to the extent to which this is possible—that is to say the axes activated by the machine control parameters are also actually present.
For gear cutting machines for the form milling or grinding of workpieces having a helicoidal generated surface, that is to say in particular spur gears, worms and rotors, such a system does not exist as yet—although it would of course also be desirable here for the reasons stated above.
The reason for this lies in a particular technical difficulty that has to be overcome in the form grinding of these workpieces: multiaxis positioning systems, as are also required by machine tools, need synchronization of the individual movements with one another, so that a defined curve is followed in three-dimensional space. This is achieved by one of the axes serving not only for its own positioning but also as a guiding axis for the synchronization of the other axes to be positioned.
Such a method according to the prior art can be found for instance in EP 0 784 525, which relates to a method of producing tooth flank modifications on bevel gears. The relevant axes are activated preferably by means of a polynomial function of the form
      f    ⁡          (      Θ      )        =            a      0        +                            a          1                          1          !                    ⁢      ΔΘ        +                            a          2                          2          !                    ⁢              ΔΘ        2              +                            a          3                          3          !                    ·              ΔΘ        3              +                            a          3                          4          !                    ·              ΔΘ        4            where f(θ) is the positioning function for the respective axis to be activated in dependence on the movement of the guiding axis θ. The coefficients a0, a1, a2, a3 and a4 serve in this case as further parameters of the position control of the respective axis activated by the function f(θ).
According to the prior art, one of the mechanical axes of the machine tool to be activated always serves in this case as the guiding axis. In the case of bevel gear cutting machines, which operate by the generating method and therefore have a cradle, as also in the case of EP 0 784 525, usually this cradle, which is always necessary, is used as the guiding axis; consequently, its generating movement is used as a guiding movement for the synchronization of the movements of the other axes. In this way there always exists—even irrespective of the further actual configuration of the respective machine type—a machine axis which, as a result of the generating process, can be used in a standard way as a guiding axis.
For form grinding machines on the other hand, which have no cradle or comparable axis, the problem of suitably choosing such a standardized guiding axis, or the question of possibly doing without it, immediately arises when attempting to standardize the machine control parameters for different machine types.
It is of course also possible here in principle to do without such a standard guiding axis and instead to specify the axis respectively used in the individual case as the guiding axis in the machine control parameters. Creating such a possibility can already lead to a certain standardization of the machine control parameters. Nevertheless, this is unsatisfactory, since, when changing a machine type to a machine which does not have the selected guiding axis, there is not only the problem of creating new machine control parameters for the guiding axis but also, on account of the dependencies described above of the other axes on the guiding axis, always the immediate requirement of generating new machine control parameters for all the other axes that are dependent on the guiding axis. If, on the other hand, there is no other axis present as the guiding axis, it can be attempted to achieve its positioning result on the workpiece by other further axes that are instead present on the new machine type being activated by machine control parameters in a corresponding way, the other axes with their respective machine control parameters remaining unaffected.
Thus, for instance, an absent positionable pivoting axis for the pivoting of the workpiece and tool with respect to each other by means of a rotation of the tool axis in the vertical can be replaced by a pivoting axis for the pivoting of the workpiece and the tool with respect to each other by means of a rotation of the workpiece axis in the horizontal, without the machine control parameters for instance of a radial infeed axis or a positionable rotating axis of a clamping head for the rotation of the workpiece in the workpiece holder being affected.
A precondition for this, however, is that a guiding axis that is standard for the entire control concept of all machine types coming into consideration can be specified. This condition is not met in the case of form grinding machines, as already stated above, if only because here—by contrast with machines which operate on the basis of a generating method—there is no generating movement that is always necessary and always able to serve as a guiding movement.